Seigerung in einem Silberblock

Ohne Zusammenfassung     

Intensification of heterogeneous catalytic gas-fluid interactions in reactors with a multichannel monolithic catalyst

The review discusses the present-day state of research, industrial experience, and prospects for application of reactors with a multichannel catalyst for gas-fluid catalytic reactions.     

Synthese de molecules encombrees : Recherche des conditions optimales de condensation dbs composes organolithiens cage sur differents substrats organiques

La réactivité des organolithiens á structure-cage vis-à-vis de trois cétones non énolisables (hexaméthyl acétone, adamantanone et benzophénone) a été testée dans différents milieux.

L'utilisation de solvants mutes (pentane-éther ou pentane-THF) est nécessaire pour que ces réactions de condensation aient lieu, mais provoque la formation de produits secondaires d'attaque sur le solvant. L'alkylation du groupe “structure-cage”, en augmentant le caractére lipophyle de la molécule, permet de solubiliser ces organolithiens dans les hydrocarbures et de mener les condensations dans ces milieux.

Les réactions de condensations avec l'hexaméthylacétone, l'adamantanone et la benzophénone conduisent respectivement à des rendements en alcool de 72, 95 et 60%, avec le triméthyl-3,5,7 adamantyl-1 lithium dans le pentane alors qu'ils ne sont que de 40, 42 et 47%, pour l'adamantyl-1 lithium dans les solvants mixtes. Les rendements optima en produit de condensation peuvent être obtenus selon les cas par la réaction de Grignard (Two-step Reaction) ou par la synthése de Barbier (One-step Alternative Grignard Reaction). Le choix entre ces deux protocoles expérimentaux dépend essentiellement de la nature de la cage dans le dérivé halogéné.

Abstract

The reactivity of bridgehead organo-lithium compounds with three nonenolisable ketones (hexamethylacetone, adamantanone and benzophenone) has been examined in various media. The condensations require use of mixed solvents (pentane-ether or pentane-THF), but secondary products are formed by solvent-attack. The alkylation of the bridgehead structure, by increasing the lipophilicity of the molecule, makes it possible to solubilise organolithium compounds in hydrocarbons and to perform condensations therein.

Condensations with hexamethylacetone, adamantanone and benzophenone lead to alcohols in yields of 72, 95 and 60%, respectively, with 3,5,7-trimethyl-l-adamanty-lithium in pentane, but only 40, 42 and 47%, for 1-adamanty-lithium in mixed solvents. The best yields of condensation product are obtained either by the Grignard reaction (two-step reaction) or by the Barbier synthesis (one-step alternative Grignard reaction). The choice between these two methods depends essentially on the nature of the cage-radical in the halide.     

Polynomial relations in the centre ofU q (sl(N))

When the parameter of deformationq is a root of unity, the centre ofU _q (sl(N)) contains, besides the usualq-deformed Casimirs, a set of new generators, which are basically themth powers of all the Cartan generators ofU _q (sl(N)). All these central elements are, however, not independent. In this Letter, generalizing the well-known case ofU _q (sl(2)), we explicitly write polynomial relations satisfied by the generators of the centre. Application to the parametrization of irreducible representations and to fusion rules are sketched.On leave from SPht, CE Saclay, 91191 Gif-sur-Yvette Cedex, France.     

Low temperature CEMS determination of the morphology of rust layers on an iron plate corroded in KCl solution

CEMS and X-ray diffraction of rust layers on an iron coupon corroded in a 0.02 M KCl solution show that there exists a magnetite layer below an outer lepidocrocite layer. The 10 K spectrum displays three ferric sextets in its lepidocrocite part with fields of 448, 422 and 387 kOe respectively. They are attributed to Fe³⁺ ions having zero, one and more Cl⁻ ions as first nearest neighbours. The Cl⁻ ions do not seem to be ordered.